TRANSLATIONAL ENERGY-DISTRIBUTIONS OF THE PRODUCTS OF THE 193 AND 157NM PHOTODISSOCIATION OF CHLOROETHYLENES

The 193 and 157 nm photodissociations of three isomers of dichloroethy lene (DCE) and trichloroethylene (TCE) were investigated using a techn ique of photofragmentation translational spectroscopy. The photofragme ntation mechanisms were constructed by analyzing the time-of-flight sp ectra of C2H2+, Cl+, HCl+, C2HCl+, and C2Cl2+, produced by electron im pact of neutral photofragments. In the 193 nm photodissociation, both the HCl elimination and the C-Cl bond rupture were important for all t he compounds examined. It was concluded that secondary dissociation of the vibrationally excited chlorinated vinyl radical produced by the C -Cl bond rupture was important even at 193 nm. In the 157 nm photodiss ociation, the mechanisms were similar to those at 193 nm for cis-DCE, 1,1-DCE, and TCE, while only the C-Cl bond rupture occurred for trans- DCE. This result suggests that the 157 nm photodissociation of trans-D CE proceeds via the direct photodissociation following the photoexcita tion to the repulsive (1)n sigma state. A minor C-H bond rupture was also found in the 157 nm photodissociations of cis-DCE and TCE. On the basis of the present mechanisms, the translational energy distributio ns and the branching ratios were estimated for all the possible proces ses. (C) 1997 American Institute of Physics.